Advancing Circularity and Carbon Neutrality in Underutilized Buildings through Adaptive Reuse and Retrofit Projects

This study investigates how Circular Economy (CE) strategies and principles can be systematically integrated across the lifecycle of Adaptive Reuse and Retrofit Projects (ARRPs) to support the low-carbon transformation of underutilized existing buildings (UEBs). While existing literature often focuses on end-product outcomes, it lacks a systematic approach for prioritizing CE principles across different project stages. Addressing this gap, the study applies the ReSOLVE framework and a Delphi method involving 19 international experts in adaptive reuse, sustainability, and heritage conservation. A mixed-methods approach combining expert elicitation, Fuzzy Synthetic Evaluation (FSE), and action mapping was used to identify and prioritize CE strategies across five lifecycle stages: Assessment, Planning and Design, Retrofitting, Operation, and Evaluation. The results highlight Optimize, Regenerate , and Exchange as the most consistently prioritized principles, with Optimize emerging as the most influential overall. The study presents a lifecycle-based decision-support framework populated with expert-informed, actionable interventions aligned with each CE principle and project phase. These interventions provide practical guidance for improving sustainability performance during the execution of ARRPs in UEBs. The research contributes a replicable model for CE strategy deployment in the built environment and offers insights for practitioners, policymakers, and researchers seeking to align adaptive reuse and retrofit with circularity and net-zero carbon objectives.